Composite membrane for desalination

Abstract

A composite membrane for desalination includes a polyethylene terephthalate (PET) nonwoven layer having a fibrous structure, and has an average thickness of about 30 to 200 micrometers (μm). A polysulfone (PS) layer having an average thickness of about 30 to 100 μm is disposed on a surface of the PET nonwoven layer. Further, a polyamide layer is disposed on a surface of the PS layer including reacted units of an acyl compound, a phenylenediamine monomer, and a poly-(DADMAC-co-DADA). The polyamide layer has a rough surface including a plurality of irregular-sized ridge-and-valley structures of polyamide. The poly-(DADMAC-co-DADA) has a formula (I), and n is a positive integer.

1 : A composite membrane for desalination, comprising:
 a polyethylene terephthalate (PET) nonwoven layer having a fibrous structure comprising a plurality of PET fibers;   wherein the PET nonwoven layer has an average thickness of about 30 to 200 micrometers (μm);   a polysulfone (PS) layer disposed on a surface of the PET nonwoven layer;   wherein the PS layer has an average thickness of about 30 to 100 μm;   a polyamide layer disposed on a surface of the PS layer comprising reacted units of an acyl compound, a phenylenediamine monomer, and a poly-(DADMAC-co-DADA);   wherein the poly-(DADMAC-co-DADA) has a formula (I), and n is a positive integer; and   
       
         
           
           
               
               
           
         
         wherein the polyamide layer has a rough surface comprising a plurality of irregular-sized ridge-and-valley structures of polyamide. 
       
     
     
         2 : The composite membrane of  claim 1 , wherein the PET nonwoven layer has an average thickness of about 50 to 100 μm. 
     
     
         3 : The composite membrane of  claim 1 , wherein the PS layer has an average thickness of about 40 to 80 μm. 
     
     
         4 : The composite membrane of  claim 1 , wherein:
 the PS layer comprises an inner sponge sublayer adjacent to and above the PET nonwoven layer, and a finger-like porous sublayer adjacent to and below the polyamide layer;   the inner sponge sublayer comprises a plurality of macro voids having an average void size of 100 to 2000 nanometers (nm); and   the finger-like porous sublayer comprises a plurality of finger-like porous structures having an average length of 20 to 50 μm, and the plurality of finger-like porous structures are vertically aligned along a surface of the composite membrane.   
     
     
         5 : The composite membrane of  claim 1 , having a water contact angle of 20 to 65°. 
     
     
         6 : The composite membrane of  claim 1 , having an arithmetical mean height (Sa) of 15 to 95 nm. 
     
     
         7 : The composite membrane of  claim 1 , having a root means square height (Sq) of 20 to 125 nm. 
     
     
         8 : The composite membrane of  claim 1 , having a maximum peak height (Sp) of 85 to 420 nm. 
     
     
         9 : The composite membrane of  claim 1 , having a maximum pit height (Sv) of −850 to −50 nm. 
     
     
         10 : The composite membrane of  claim 1 , having a permeation flux of 20 and 60 L/m 2  hr. 
     
     
         11 : The composite membrane of  claim 1 , having a salt rejection of at least 90% based on an initial weight of the salt in a salt solution. 
     
     
         12 : A method of making the composite membrane of  claim 1 , comprising:
 mixing monomers of diallydimethylammonium chloride (DADMAC), N 1 , N 1 -diallyldodecane-1,12-diammonium chloride (DADAC) in a first solvent in the presence of 2,2′-Azobis(2-methylpropionamidine) dihydrochloride (AMPD) to form a first mixture;   heating the first mixture thereby polymerizing the monomers of DADMAC and DADAC to form a poly-(DADMAC-co-DADAC) of formula (II) in a first crude mixture;   
       
         
           
           
               
               
           
         
         dialyzing the poly-(DADMAC-co-DADAC) in the presence of a base and drying to form the poly-(DADMAC-co-DADA); 
         mixing and dissolving a polysulfone (PS) polymer in a second solvent and degassing to form a PS solution; 
         drop casting the PS solution onto the surface of the PET nonwoven layer to form a sample containing a PS liquid layer; 
         immersing the sample in a liquid medium thereby precipitating the PS polymer from the PS solution to form the PS layer disposed on the surface of the PET nonwoven layer; 
         removing the sample from the PS solution, washing and drying; 
         dipping the sample after the drying in a second mixture containing the phenylenediamine monomer, and the poly-(DADMAC-co-DADA); and 
         contacting the sample after the dipping with a third mixture containing the acyl compound thereby polymerizing to form the polyamide layer on the surface of the PS layer. 
       
     
     
         13 : The method of  claim 12 , wherein the base is at least one selected from the group consisting of NaOH, KOH, LiOH, and Ca(OH) 2 . 
     
     
         14 : The method of  claim 12 , wherein the polysulfone polymer has a weight average molecular weight (M w ) of 35,000 g/mol, and a number average molecular weight (M n ) of about 16,000 g/mol. 
     
     
         15 : The method of  claim 12 , wherein the second solvent is at least one selected from the group consisting of dimethylacetamide (DMA), dimethylformamide (DMF), and dimethyl sulfoxide (DMSO). 
     
     
         16 : The method of  claim 12 , wherein the PS polymer is present in the PS solution at a concentration of 5 to 40 wt. % based on a total weight of the PS solution. 
     
     
         17 : The method of  claim 12 , wherein the phenylenediamine monomer is m-phenylenediamine (MPD). 
     
     
         18 : The method of  claim 12 , wherein the acyl compound is trimesoyl chloride (TMC). 
     
     
         19 : A desalination process, comprising:
 passing a liquid through the composite membrane of  claim 1 , wherein the liquid is at least one selected from the group consisting of salty water, ocean/sea water, rejected brine, wastewater, brackish water, flowback/produced water, and waste flows.   
     
     
         20 : The desalination process of  claim 19 , wherein the liquid is a salty water containing sodium chloride (NaCl), and wherein the NaCl is present in the salty water at a concentration of 1 to 20 grams per liter (g/L) based on a total volume of the salty water.